3D Electron Density Reconstruction from the SECCHI White Light Coronagraphs Onboard Stereo

The twin STEREO spacecraft will carry onboard the SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation) experiment, consisting of an EUVI disk imager and three white light coronagraphs on each spacecraft. At NRL we are investigating the tomographic electron density reconstructions, and their limitations, that are achievable from just two viewpoints using the coronagraph observations. We discuss our reconstruction technique and show results from our current work. We started with geometrically simple constant density objects (cylinders, half-shells), and have proceeded on to several CME numerical models we have obtained from cooperating colleagues. We render from the starting known electron density distribution a perfect white light image, in radial and tangential polarizations, typically from two viewpoints in the elliptic plane, and then add noise. Using these input synthetic observations, we employ our PIXON reconstruction technique to produce a best (using fewest PIXON elements) electron density reconstruction that reproduces the input images. We discuss the agreement of the PIXON reconstructions with the known starting model electron density distributions which produced the input images. We are particularly interested in the limitations present when only two viewpoints are available. The reconstructions are significantly improved with the addition of a third viewpoint to the reconstruction, such as could be provided during the STEREO mission by an operating LASCO coronagraph on the SOHO spacecraft. Information on our project can be found from the web site http://stereo.nrl.navy.mil. This work is supported by NASA under S-13631-Y, and by the Office of Naval Research. The SECCHI experiment is an international collaboration led by the Naval Research Laboratory.